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To allow climate change impact assessment on river system water quality, the scientific community lacks efficient deterministic models able to simulate hydrological and biogeochemical processes in drainage networks at the regional scale, with a fine temporal resolution and with water temperature explicitly determined. The model QUALity-NETwork (QUAL-NET) was developed and tested on the Middle Loire River Corridor, a sub-catchment of the Loire River (France), prone to eutrophication. Hourly variations computed by the model helped disentangle the complex interactions existing between hydrological and biological processes across different timescales. Phytoplankton variations in the Loire River were governed by phosphorus availability and transit time. Model QUAL-NET showed that a large amount of phytoplankton cells growing in the upper part of the studied corridor was recycled through the microbial loop, which enhanced phytoplankton growth, explaining why severe blooms still occur in the Loire River despite large P input reductions. [ABSTRACT FROM AUTHOR]

Concentration of trace elements both in the water column (dissolved phase and acid-soluble suspended particles) and in sediments (bulk and acid-soluble particles) was followed for one year in a water reservoir (the Bicaz reservoir) used for electricity production. This study investigated the impact of river inflows, outflows and the position of the outflow for the cycling and the transport of these elements along this water reservoir. Time series results reveal that river inflow supplies mainly reducing waters. In the water column, the stable Al/Fe ratio (from 0.8 to 1.5) recorded in acid-soluble suspended particles suggests the formation of similar amorphous phases during the year, phases that could be stabilized by organic ligands. In sediments, these amorphous phases are no more recorded. In the water column, some trace elements are strongly associated with Al-Fe amorphous phases (Rb, Cs, Co, Cu, Zn, Pb, Th); others are independent (Sr, Sn, As, Sb, U). In sediments, Co, Y, Zn, Ga, Cr, Ni, V, Rb, and Ba are associated with phases containing Fe, Al, K, Mg, P and Ti. The reservoir acts as a moderate sink for Fe, V, Cr, Co, Cu; it acts alternately as a sink and a source for Zn. Among the elements studied, only Mn and Ni are significantly stored. Rb shows particular affinity for Fe oxide which is not recorded in literature. Our results show the importance of the outflow depth on the transport of trace elements within a reservoir. [ABSTRACT FROM AUTHOR]

The Kaluvelly watershed is a coastal area (Tamil Nadu, India) where water abstraction has resulted in a dramatic fall in the level of the water table and a piezometric depression in the most exploited aquifer, the Vanur aquifer. In addition, intensification/mechanization of agriculture may have affected the quality of recharge water. An initial hydrodynamic study showed that the Vanur aquifer is highly vulnerable to salinization due to potential seawater intrusion, and our aim was to determine the source of salinity recorded in the groundwater of this multilayered aquifer. Our approach involved the use of existing boreholes and of a moderate number of samples, with the aim of developing appropriate water resource management techniques. Major element, 18O/16O, 2H/1H and 87Sr/86Sr, ratios were measured in rainwater, surface water and groundwater collected during five sampling campaigns over a 2-year period. Geochemical data indicate that the Vanur aquifer is recharged and that small mixings between aquifers fluctuate according to monsoon intensity. There was no evidence of seawater intrusion. The range of recorded salinity originated mainly from water-rock interaction but a disconnection of some deeper parts of the aquifer was apparent. Strontium isotopic ratios in the recharge area suggest an anthropogenic influence, possibly related to fertilizer use. A high SO4/Cl ratio was observed in the aquifer; in the deeper parts, the influence of a formation containing lignite is hypothesized, whereas near the surface, sulphate may partly originate from fertilizer use and fossil fuel combustion. Water isotopic data suggest that the origin of precipitation in this region has been unchanged for several hundreds or thousands of years. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]